Heretofore, the resistance spot brazing has widely and generally been employed to braze the aluminum article portions one to another. In this method, electrodes made of copper or the like are set in contact with the portions which are to be brazed, and an electric current is supplied through said portions which are pressed to each other. Resistance heat which the current generates is utilized to raise the temperature of the article portions to be brazed. Further, the so-called torch brazing and high-frequency brazing are also practiced.
It is however noted that the intrinsic electrical resistance of aluminum is considerably low and the heat conductivity of aluminum is so high that only a limited amount of heat is generated by the electric current. Therefore, a heavy current for example 20 to 30 kA is needed for each spot to produce a sufficient amount of heat for the brazing, thereby raising its energy cost. In addition, an alloy of copper and aluminum will inevitably be produced at the tip ends of electrodes. Such an alloy causes the dressing of said electrodes to be done frequently, resulting in an earlier wear and tear of the electrodes and a lower productivity of the brazing. Due to the abraded electrodes and the variable surface state of the aluminum articles, the brazed strength thereof is likely to vary between the brazed products, thus impairing their reliability in quality. It is another problem that material consumption increases because of broader regions of the articles overlapped one on another for a higher current density.
In the torch brazing or the high-frequency brazing of large articles, it has been extremely difficult to heat and simultaneously press their portions to be brazed, due to their great dimension. Thus, they cannot be adjoined one to another, or their brazed strength varies beyond a permissible range even if the brazing itself is possible. The poor heat efficiency in these brazing methods has particularly rendered it difficult to braze those materials which are made of an alloy of aluminum and magnesium.
The present invention was made to resolve such problems as mentioned above, and therefore an object of the invention is to provide a novel method of hot brazing the aluminum articles not only efficiently in general but also effectively in the partial adjoining of large-sized articles, without failing to ensure their brazed strength.